Solid mixtures of alpha-hydroxycarbonyl derivatives of alpha-methylstyrene oligomers and their use

ABSTRACT

The present invention refers to solid mixtures of alpha hydroxycarbonyl derivatives of alpha-methylstyrene oligomers containing at least 90% of the dimer isomers, the dimer isomer ratio being between 2.5 and 7, to their preparation and to their use as photoinitiators in photopolymerisation.

[0001] The present invention refers to solid mixtures ofalpha-hydroxycarbonyl derivatives of alpha-methylstyrene oligomers andto their use as photoinitiators in light-induced radicalphotopolymerisation of acrylic systems.

[0002] In particular the invention refers to the preparation of thesolid mixtures, which can be easily handled and which mainly contain oneof the dimer isomers.

[0003] According to a fundamental aspect of the invention it wassurprisingly found that the solid mixtures exhibit an higher reactivitythan the one expected from the purity of the dimer isomers.

[0004] The use of oligomeric photoinitiators in the photopolymerisationhas several advantages in comparison to the use of monomericphotoinitiators, such as a lower migratability of the photoinitiatorfrom the formulation and a reduced amount of volatile compounds derivedfrom their photodecomposition.

[0005] Those characteristics are important for the industrial usebecause they reduce the risk of contamination of the finished productwith unwanted compounds.

[0006] Among oligomeric photoinitiators the alpha-hydroxycarbonylderivatives of dimers and trimers of alpha-methylstyrene are known.

[0007] These photoinitiators are described, for instance, in U.S. Pat.No. 4,987,159.

[0008] They are mainly constituted by a mixture of dimer and trimerisomers.

[0009] At room temperature the mixture is a very highly viscous productthat cannot be easily used as such in industrial applications.

[0010] In the present text with the expression “alpha-hydroxycarbonylderivatives of oligomers of alpha-methylstyrene” we refer to compoundsof Formula I, wherein n is a number equal or greater than 0.

[0011] The alpha-hydroxycarbonyl derivatives of oligomers ofalpha-methylstyrene are a product with a pour point of from 40 to 50° C.In the present text, this product is indicated as “high viscositymixture”.

[0012] Another aspect of the invention is a process for theprecipitation of a solid mixture from said high viscosity mixture.

[0013] According to another aspect of the invention the solid mixtureobtained by precipitation from the high viscosity mixture mainlyconsists of the dimer isomers in a modified ratio.

[0014] In particular the concentration of dimer isomers 5 and 6increases from 60-85% (w/w) in the high viscosity mixture to about90-98% (w/w) in the solid mixture and the ratio of the dimer isomers 5and 6 from 1.5-2.3 to 2.5-7.0.

[0015] The expression “dimer isomer 5” refers to the product of FormulaII.

[0016] The expression “dimer isomer 6” refers to the product of FormulaIII.

[0017] In patent U.S. Pat. No. 4,987,159, the Applicant describes aprecipitation of the mixture of alpha-hydroxycarbonyl derivatives ofdimers and trimers of alpha-methylstyrene, without reporting amodification of the ratio between the dimer isomers 5 and 6 in theobtained mixture.

[0018] According to a fundamental aspect of the present invention, thesolid mixtures of alpha-hydroxycarbonyl derivatives of oligomers ofalpha-methylstyrene containing at least 90% of the dimer isomers 5 and 6are disclosed, the ratio of the dimer isomer 5 and the dimer isomer 6being between 2.5 and 7.

[0019] Another aspect of the present invention is a process for thepreparation of the solid mixtures exhibiting an higher reactivity thanthe one due to the increase in purity.

[0020] This behaviour suggests that the reactivity of the dimer isomersis regiospecific.

[0021] The solid mixtures of alpha-hydroxycarbonyl derivatives ofoligomers of alpha-methylstyrene of the present invention are obtainedby precipitation from a high viscosity mixture containing at least 60%of the dimer isomers of the above mentioned derivatives.

[0022] Such high viscosity mixture can be prepared as reported forinstance in U.S. Pat. No. 4,987,159.

[0023] The process for the preparation of the solid mixtures ofalpha-hydroxycarbonyl derivatives of oligomers of alpha-methylstyrene ofthe present invention consists in dissolving the high viscosity mixtureof alpha-hydroxycarbonyl derivatives of oligomers of alpha-methylstyrenein a solvent with a polarity between 0.1 and 0.7, preferably between0.25 and 0.6, with a ratio solvent/high viscosity mixture between 0.2and 4, preferably between 0.4 and 2.5, keeping the solution at atemperature below 40° C. for from 10 to 60 hours and collecting the thusobtained solid mixture.

[0024] The polarity of the solvent (ε°) corresponds to the absorptionenergy measured on Al₂O₃.

[0025] According to a further aspect of the invention the use in radicalphotopolymerisation of formulations containing at least one unsaturatedcompound of the solid mixtures of alpha-hydroxycarbonyl derivatives ofoligomers of alpha-methylstirene, containing at least 90% of the dimerisomers 5 and 6, the ratio of the dimer isomers 5 and 6 being between2.5 and 7 is disclosed.

[0026] The solid mixtures of the present invention are particularlysuitable in photopolymerisation of formulations containing unsaturatedcompounds of the class of acrylic or methacrylic derivatives, ormixtures thereof, and are preferably used as photoinitiators in lowyellowing paints and laquers, in adhesives, in photocrosslinkablecompositions for printing plates and in the field of graphic arts.

[0027] The isomer 5 has a higher reactivity than the isomer 6 inphotopolymerisation.

[0028] Such higher reactivity is demonstrated by the fact that theincrease of the solid mixture of the invention is higher of at least 2%than the increase of the content of dimer isomers in the same mixture.

[0029] This is a surprising result, because at our knowledge aregiospecific activity had never been found before in photoinitiators.

[0030] In the following examples the measurement of the content of thedimer isomers and of the ratio between the two dimer isomers 5 and 6 inthe high viscosity mixtures and in the solid mixtures reported inexamples was carried out by HPLC (high performance liquidchromatograpy). The chromatographic conditions were: column C18, 4 μm,150×3.9 mm; eluent: solvent A=methanol, solvent B=water; gradient from70% A to 100% A in 10 min, 100% A 10 min; flow rate 0.8 ml/min, detectorUV 254 nm.

EXAMPLE 1

[0031] The precipitation of the solid mixture is carried out withtoluene as solvent (ε° 0.29) using a high viscosity mixture with a dimercontent of 85.1% and a ratio between the dimer isomers 5 and 6 of 1.93.This high viscosity mixture (Mixture 1) was obtained as reported inExample 10 of the patent U.S. Pat. No. 4,987,159.

[0032] 14 kg of toluene are transferred into a heated reactor, set at atemperature of 120° C., and 28 kg of Mixture 1 are added under stirring.After complete dissolution the temperature is set at 20° C. and a smallportion of a previously precipitated product is added.

[0033] The precipitation mixture is left at 20° C. under stirring for 48hours. The precipitate is filtered on a buckner and washed twice withtoluene.

[0034] The amount of dried precipitate is 11.8 kg (Solid Mixture 1,yield 41.3%); the content of the dimer isomers is 96.8% and the ratio ofthe dimer isomers 5 and 6 is 2.93

EXAMPLE 2

[0035] The precipitation of the solid mixture is carried out using ethylacetate (ε° 0.58) as solvent and according to Example 1, using 1000 g ofMixture 1 and 500 g of ethyl acetate, at a dissolution temperature of75° C., and at a precipitation temperature of 22-24° C. for 48 hours.

[0036] The amount of dried precipitate is 451 g (Solid Mixture 2, yield45.1%); the content of the dimer isomers is 93.2% and the ratio betweenthe dimer isomers 5 and 6 is 2.5.

EXAMPLE 3

[0037] Evaluation of the Photopolymerisation Reactivity of Solid Mixture1

[0038] A formulation based on 75% (w/w) of Ebecryl 220 (urethaneacrylate oligomer from UCB), 12.5% (w/w) of propoxylated gliceroltriacrylate and 12.5% (w/w) of hexanediol diacrylate was prepared and 4%(w/w) of Solid Mixture 1 was added under stirring at room temperature.

[0039] A layer of 50 μm of the photoinitiated formulation was spreadedon a cardboard and cross-linked using a Giardina® apparatus equippedwith a medium pressure mercury lamp of 80 W/cm. The maximum speed ofcross-linking was 17.0 m/min. The photopolymerisation is consideredcomplete when the formulation resists to the surface abrasion (it is notdamaged after repeated brushing using a sheet of paper pressed by athumb).

EXAMPLE 4

[0040] Evaluation of the Photopolymerisation Reactivity of Mixture 1

[0041] A formulation based on 75% (w/w) of Ebecryl 220 (urethaneacrylate oligomer from UCB), 12.5% (w/w) of propoxylated gliceroltriacrylate and 12.5% (w/w) of hexanediol diacrylate was prepared and 4%(w/w) of Mixture 1 was added under stirring at room temperature.

[0042] A layer of 50 μm of the photoinitiated formulation was spreadedon cardboard and cross-linked using a Giardina® apparatus equipped witha medium pressure mercury lamp of 80 W/cm. The maximum speed ofcross-linking, measured according to Example 3, was 14.5 m/min.

[0043] Comparing the results of Examples 3 and 4, an increase of contentof the dimer isomers of 13.7% results in an increase of reactivity of17.2%.

[0044] This difference shows a surprisingly higher reactivity of isomer5 compared to isomer 6.

1. Solid mixtures of alpha-hydroxycarbonyl derivatives of oligomers ofalpha-methylstyrene characterised by the fact that they contain at least90% of the dimer isomers 5 and 6, the ratio of the dimer isomer 5 andthe dimer isomer 6 being between 2.5 and
 7. 2. Solid mixtures ofalpha-hydroxycarbonyl derivatives of oligomers of alpha-methylstyreneaccording to claim 1, obtained by precipitation from a mixturecontaining them.
 3. Solid mixtures of alpha-hydroxycarbonyl derivativesof oligomers of alpha-methylstyrene according to claim 2, obtained byprecipitation from a mixture containing at least 60% of the dimerisomers 5 and
 6. 4. Process for the preparation of solid mixtures ofalpha-hydroxycarbonyl derivatives of oligomers of alpha-methylstyrenecontaining at least 90% of dimer isomers 5 and 6, the ratio of the dimerisomer 5 and the dimer isomer 6 being between 2.5 and 7, consisting indissolving an high viscosity mixture of alpha-hydroxycarbonylderivatives of oligomers of alpha-methylstyrene in a solvent with apolarity between 0.1 and 0.7, with a ratio solvent/mixture between 0.2and 4, keeping the solution at a temperature below 40° C. for from 10 to60 hours and collecting the thus obtained solid mixture.
 5. Use of thesolid mixtures of alpha-hydroxycarbonyl derivatives of oligomers ofalpha-methylstyrene containing at least 90% of the dimer isomers 5 and6, the ratio of the dimer isomer 5 and the dimer isomer 6 being between2.5 and 7 in the photopolymerisation of formulations containing at leastone unsaturated compound.